Caring For Bearded Irises In Late Summer: Expert Tips From Our Professional Gardener

Bearded irises (Iris germanica) are vigorous perennials that bloom in spring in a rainbow of colors (in fact, the name iris refers to the Greek goddess of the rainbow). Bearded irises increase in size every year, and though they're not very fussy plants, they do need proper care to flourish. As a professional gardener, I often add irises to clients' flower gardens for vivid spring beauty. There are several easy but important tasks to do in late summer to care for bearded irises to keep them thriving.

These tasks include trimming, dividing, replanting, and improving the existing iris bed. I tend to divide bearded irises every other year, since they often double in size each year once established. Most bearded iris varieties can be trimmed and divided starting in August. If you have reblooming varieties, wait until the last blooms have faded, closer to early autumn, then trim and/or divide as usual.

If your iris plants aren't flowering like they used to despite dividing, they may need more sun or more space, and this is the perfect time to relocate them. It's also important to remember to plant them at the right depth. Some of the tuber should be visible above the ground, exposed to sunlight: This helps the plant absorb nutrients and form flower buds. Irises aren't too fussy about soil, but I find that a loamy, somewhat sandy, well-drained soil will keep them very happy.

Some gardeners trim their iris leaves right after spring blooming, while others cut the flower stems and let the spiky green leaves flourish through the summer. I usually trim them once the leaves start to droop and turn yellow or brown to keep the garden looking fresh in late summer. If dividing them, you should trim both the leaves and the tubers after digging them up. Use clean bypass pruners to trim the rhizomes, removing any rotted, mushy, or dried-out segments. Then I trim the leaves to about 3 to 4 inches long.

Bearded irises are easy to divide. Dig them up, shake off excess soil, gently break apart large clumps, then trim the tubers and leaves with bypass pruners. If you divide them but don't get around to re-planting right away, don't worry. Keep them in a shaded, dry place. The trimmed leaves may naturally dry out or curl a bit as they go dormant. They should re-establish themselves as long as you plant them before the first hard frost. In upstate New York, I try to get them replanted by mid-October at the latest. 

When relocating irises or adding more, choose a sunny spot where they have room to spread. They prefer full sun, but will adapt fairly well to partial sun. Don't mulch your irises: They thrive best when the tubers get plenty of sun and air, as this promotes flowering and prevents rotting. Irises shouldn't need fertilizing if your soil is healthy. Add some soil amendments or conditioners (a bit of compost or aged manure) when you replant in late summer to give them a boost.